The Nepal earthquake that has killed at least 1,500 people was a 'nightmare waiting to happen', disaster experts said last night.

Just a week ago, 50 earthquake scientists from around the world met in the capital Kathmandu to work out how to prepare the congested, overdeveloped and shoddily-built area for a massive earthquake like the one seen today.

They knew they were racing the clock, but they did not know when what they feared would strike.

Today's tragedy has left more than 1,500 people are dead, with hundreds more missing - including up to 50 Britons - after the 7.8 magnitude earthquake and the mount Everest avalanche it triggered.

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A man buried up to his shoulders in rubble is rescued from the remains of a destroyed building in Kathmandu, Nepal, after the earthquake, which was was a 'nightmare waiting to happen' according to disaster experts

Locals rescued two more dust-covered men, pulling them up on the the street as they work to find and rescue any survivors of the disaster

Just a week ago, 50 earthquake and social scientists from around the world met in the capital Kathmandu (rubble in the city pictured) to work out how to prepare the congested, overdeveloped and shoddily-built area for a massive earthquake

People search for survivors in the rubble of a destroyed building after the earthquake hit Nepal and surrounding countries at just after 6am GBT time

'It was sort of a nightmare waiting to happen,' said seismologist James Jackson, head of the earth sciences department at the Cambridge University. 'Physically and geologically what happened is exactly what we thought would happen.

'I was walking through that very area where that earthquake was and I thought at the very time that the area was heading for trouble,' said Mr Jackson, lead scientist for Earthquakes Without Frontiers, a group that tries to help Asian cities prepare for disasters.

A Kathmandu earthquake has long been feared, not just because of the natural seismic fault, but because of the local, more human conditions that make it worse.

Earthquakes of similar magnitude can have bigger effects on different parts of the globe because of the manner of building construction and population density.

A 7.8 magnitude earthquake could kill 10 to 30 per one million residents in California, but has killed at least 1,500 in Nepal, and could kill up to 10,000 in parts of Pakistan, India, Iran and China, said U.S. Geological Survey seismologist David Wald.

This is the fifth significant earthquake in Nepal in the last 205 years, including a massive one in 1934 that levelled the city.

Missing: Tara Bradshaw, 24, from Brighton, is among the Britons who have not been heard from since the devastating earthquake

33-year-old Google executive Dan Fredinburg is among the 18 climbers confirmed killed in the avalanche on Mount Everest

Devastating: At least 18 climbers were killed after the earthquake which buried tents at the base camp of Everest (pictured)

The United States Geological Survey said the quake struck 81 kilometres (50 miles) northwest of Kathmandu at 06.11 GMT, with walls crumbling and families racing outside of their homes

Nepalese rescue teams remove a body from the rubble of the historic 19th century Darahara Tower in Kathmandu which collapsed in the quake

People search for survivors in the rubble of a destroyed building after the earthquake hit Nepal and surrounding countries at just after 6am GBT time

People carry a woman from the rubble of a destroyed building while locals and rescue teams continue to search for more survivors of the earthquake

WHAT HAPPENED? AND WHAT HAPPENS NEXT?

Seismologist Earle said the quake happened on what is known as a 'thrust fault.'

That describes the situation when one piece of the Earth's crust is moving beneath another piece.

In this case, it's the Indian plate that is moving north at 45 millimeters (1.7 inches) a year under the Eurasian plate to the north, Earle said. It's a different type of earthquake than the one that caused the 1906 San Francisco earthquake.

'This is what builds the Himalayan mountain range,' Earle said.

The region and particular fault has a history of damaging earthquakes, including four temblors with magnitudes greater than 6.0 in the past 100 years, Earle said, warning that landslides are a particular worry now, given the steep slopes in the region.

'They knew they had a problem but it was so large they didn't where to start, how to start,' said Hari Ghi, south east Asia regional coordinator for Geohazards International, a group that calculates worldwide quake risks. Nepal was making progress on reducing its vulnerability to earthquakes, but not quickly or big enough.

Mr Ghi's group, on April 12, updated a late 1990s report summarising the Kathmandu Valley risks.

'With an annual population growth rate of 6.5 per cent and one of the highest urban densities in the world, the 1.5 million people living in the Kathmandu Valley were clearly facing a serious and growing earthquake risk,' the report said, laying out 'the problem' the valley faces.

'It was also clear that the next large earthquake to strike near the Valley would cause significantly greater loss of life, structural damage, and economic hardship than past earthquakes had inflicted.'

And for years there were no building codes and rampant development so homes and other structures could be built without any regards to earthquakes, the report said. There are now building codes, but that doesn't help the older structures, and the codes aren't overly strong, Mr Ghi said.

It's actually even made worse because of local inheritance laws that require property be split equally among all sons, Mr Jackson said. So that means buildings are split vertically among brothers making very thin rickety homes that need more space so people add insecure living space on additional floors, he said.

'The construction is appalling in Kathmandu,' he said.

Poverty and pollution make the problem worse. That's because people don't spend time worrying about some future earthquake because they have more pressing problems.

'If you live in the Kathmandu Valley you have other priorities, daily threats and daily nasty things happen to you in terms of air quality, water quality, pollution, traffic and just poverty,' Mr Jackson said. 'But it doesn't mean that the earthquakes go away.'

The earthquake had an epicentre 80 kilometres north-west of Kathmandu,according to United States Geological Survey and strong tremors were also felt in large areas of northern and eastern India and Bangladesh

A man comforts a woman next to a seriously injured person on the ground in the aftermath of the disaster which is thought to have killed at least two

Nepal rocked by 7.9 magnitude earthquake

Volunteers help remove a huge pile of debris from what used to be a building in Durbar Square before the quake which caused extensive damage with toppled walls and collapsed buildings

Huge teams of locals and volunteers help to heave away huge pieces of debris from homes, business and offices left by the earthquake

Panicked residents had rushed into the streets as the tremor erupted with the impact felt hundreds of miles away in big swathes of northern India and even in Bangladesh.

Video footage showed people digging through the rubble of the bricks from the collapsed tower, looking for survivors.

Nepal’s capital Kathmandu – with a population of over one million – was one of the worst-hit areas in Nepal, with the quake’s epicentre just 50 miles north of the city. As the tremors intensified, people were seen in scenes of mayhem running from their homes and places of work in panic.

Dozens of people were gathered in the car park of Kathmandu's Norvic International Hospital, where thin mattresses had been spread on the ground for patients rushed outside, some patients wearing hospital pyjamas, while doctors and nurses were treating people.

The United States Geological Survey said the quake struck 81 kilometres (50 miles) northwest of Kathmandu at 06.11 GMT, with walls crumbling and families racing outside of their homes. The 7.8 magnitude tremor was the worst to hit the poor South Asian nation in over 80 years.

Television footage showed a huge swathe of houses had collapsed in while roads had been split in two by the force of the impact.

India was first to respond to Nepal's appeal for help by sending in military aircraft with medical equipment and relief teams.

Britain has deployed a team of humanitarian experts to Nepal to provide urgent support for people affected by the quake, International Development Secretary Justine Greening announced tonight.

Ms Greening said: 'My thoughts are with the people of Nepal, in particular all those who have lost loved ones.

'The absolute priority must be to reach people who are trapped and injured, and provide shelter and protection to those who have lost their homes.

'Nepal needs our urgent humanitarian assistance. That is why we have rapidly deployed a team of humanitarian experts who will immediately begin work assessing the damage and helping the Nepalese authorities respond to this devastating earthquake.'

It came after Prime Minister David Cameron pledged that the UK would do all it can to help in the aftermath on the Nepal earthquake.

On Twitter he said: 'Shocking news about the earthquake in Nepal - the UK will do all we can to help those caught up in it.'

Foreign Secretary, Philip Hammond, added his condolences and said the British Embassy was providing help to any UK nationals caught up in the disaster.

'My thoughts are with the people of Nepal and everyone affected by the terrible loss of life and widespread damage caused by the earthquake,' he said.

'We are in close contact with the Nepalese government. The British Embassy in Nepal is offering our assistance to the authorities and is providing consular assistance to British Nationals.'

The shallow earthquake measuring 7.8 magnitude struck west of the ancient Nepali capital of Kathmandu on Saturday, killing more than 1,500 people and demolishing buildings

A collapsed house in Nyelam County in Shigatse, Tibet (left) while a man looks through the ruble of a similarly damaged building in Kathmandu

As well as leveling many of Kathmandu's homes and structures, the quake also left a dust pall over the valley, doctors and witnesses said

People search for survivors under the rubble of collapsed buildings in Kathmandu Durbar Square, a UNESCO sitem after an earthquake caused serious damage

A huge clean up and rescue effort is underway to find survivors of the tragedy and to try and clear away debris from the toppled walls and collapsed buildings